Multistep Dissolution of Lamellar Crystals Generates Superthin Amorphous Ni(OH)₂ Catalyst for UOR

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Urea oxidation reaction (UOR) is a promising alternative to oxygen evolution reaction (OER) for hydrogen production due to favorable thermodynamics.
• Nickel-based catalysts are crucial for UOR, but their activity is limited by the high oxidation potential required to form the active Ni³⁺ species.

Purpose of the Study:

• To investigate the mechanism of nickel molybdate hydrate dissolution for catalyst preparation.
• To develop a highly active amorphous nickel (II) hydroxide (ANH) catalyst for urea oxidation reaction (UOR).

Main Methods:

• In situ cryo-transmission electron microscopy (cryoTEM)
• Cryo-electron tomography
• In situ Raman spectroscopy
• Theoretical calculations

Main Results:

• A multistep dissolution process of nickel molybdate hydrate was elucidated, leading to the formation of superthin, amorphous nickel (II) hydroxide (ANH) flocculi.
• The ANH catalyst exhibits significantly enhanced UOR activity compared to conventional Ni(OH)₂, with over an order of magnitude higher current density (640 mA cm⁻²).
• The ANH catalyst demonstrates 30 times higher mass activity and 27 times higher turnover frequency (TOF) than Ni(OH)₂.

Conclusions:

• The multistep dissolution mechanism provides an effective route for synthesizing highly active amorphous catalysts.
• The developed ANH catalyst offers a superior alternative for efficient hydrogen production via UOR.